How to generate patches with git format-patch

git-format-patch prepares e-mail-ready version of patches. In its basic invocations, it will create a .patch file per commit, of the form 000X.First_line_of_commit_message.patch, where X is the number of the commit in the commit series.

What git format-patch master does is look at the commits between master and your current branch, in this case Issue-#344, and create a patch file per commit. git format-patch master..Issue-#344 means the same thing: make patches for the commits between master and Issue-#344.